CHEMISTRY COMMUNITY

Beza Ayalew 1I

no, as long as your T1 and k1 are corresponding

Beza Ayalew 1I

I'm assuming it will increase but I'm not 100% sure

Beza Ayalew 1I

if the slow step is the first step, I don't know if you still have to keep track of intermediates?

Beza Ayalew 1I

does that mean spontaneous solutions in general will have metals dissolve in the solution?

Beza Ayalew 1I

The reaction with the higher activation energy is the slow reaction, I'm not 100% sure, but if he doesn't explicitly say which is fast and which is slow I think that should be helpful as well.

Beza Ayalew 1I

For that question I was also wondering if we would be given the formula on the final formula sheet? I don't think I saw it on the formula sheet posted on the 14B website

Beza Ayalew 1I

Can someone explain to me how to do 15.23 part c? Specifically why you would subtract by .153 when you convert the change in concentration of B to moles per liter of A?

Beza Ayalew 1I

I just realized this isn't what the solutions manual did, but it's what made the most sense to me personally

Beza Ayalew 1I

Just like in 17, you use the 2 rows where Bs concentration is changing, but As and Cs concentrations are not, which in this case would be experiments 1 and 3. Then you can divide the 2 different B concentrations to get a number to the power of n, and then divide the initial rates to solve for what t...

Beza Ayalew 1I

One thing I was confused on was where the 2 came from, so the 2 is because of the stoichiometric coefficient of the reactant? What if there was more than one reactant?

Beza Ayalew 1I

Because all of the graphs he showed were linear, there would be no instance where there is exponential growth or decay?

Beza Ayalew 1I

the solution doesn't plug in 20mg as the initial concentration, but if you do that the same values come out, and i found doing that easier to grasp because you can just directly solve for the final concentration

Beza Ayalew 1I

Is or when is a time when you would need to use both?

Beza Ayalew 1I

if you used the standard potentials from the equations given on the back of test and didn't flip the signs, and didn't confuse the cathode vs the anode, your work is fine so your answer should be right

Beza Ayalew 1I

I think they would give you some information or if any assumptions were made, it would probably be for reactions we should know, like combustions where we automatically know O2 is a reactant and H2O is a product

Beza Ayalew 1I

I personally have a habit of changing mmol/L to just mol/L, but the solutions usually leaves it as mmol/L if that's how it was given in the problem, but I'm assuming unless they explicitly ask for a certain unit or you're solving for the rate which is usually in moles and seconds, it shouldn't matter?

Beza Ayalew 1I

Because C is the zeroth order, it's concentration does not change the rate at all, so it's not added to the rate law because the concentration of C doesn't affect the rate. However, I'm not exactly sure if you would be deducted points for including [C]^0 on a test in the rate law equation

Beza Ayalew 1I

So the test doesn't include the slow and fast reactions, right?

Beza Ayalew 1I

Also can someone explain why you have delta nRT, but not nRdeltaT? I feel like I've seen the second one being used but usually the change goes towards the number of moles.

Beza Ayalew 1I

if you're using delta v, you're probably going to be using delta nRT, so that something to consider as well

Beza Ayalew 1I

I don't think it's gong to be worded the way it was on the practice exam, but you're probably going to need to know the logistics for a conceptual problem.

Beza Ayalew 1I

On Monday we started the section on electrochemistry, which is basically redox reactions and batteries and the like. He introduced galvanic cells and later cell potential an electromotive force. Lucky for you, we won't have those topics on the midterm, which will just be on thermochemistry and therm...

Beza Ayalew 1I

Does it also tell us that the reaction is able to happen without an addition of energy?

Beza Ayalew 1I

I think its just negatively charged ions, anions, that are transferred in the salt bridge because the point is to more or less "cancel out" the increase in negative charge going in the direction of the current

Beza Ayalew 1I

I think it has to do with where he mentioned that without a potential difference, the battery ceases to function, so there needs to be some potential difference for the battery to continue to work and as it approaches zero, the battery does not transfer electrons or ions and the battery needs to be ...

Beza Ayalew 1I

I think the sheet Dr. Lavelle gives on the exams says the conversion is 273.15 so I would suggest using that

Beza Ayalew 1I

I think it has to do with the idea we learned in Chem 14A that to create more product, you would remove products so that the system creates more in an attempts to have the products and reactants at an equilibrium, so when you remove or have few products, the system replenishes the product needed to ...

Beza Ayalew 1I

Hey, I'm a little confused on where the addition of 1.48x10^4J came from in number 19. Is it because of the phase change and if so, why that number?

Beza Ayalew 1I

Also does this mean we are expected to know which state any given substance will be in at an average of 25 degrees C?

Beza Ayalew 1I

So if a substance is not in standard state then we do a phase change or change the pressure?

Beza Ayalew 1I

Sorry this is a little off topic but does this make Internal energy, or the change in internal energy not a state function because both heat and work are not state functions?

Beza Ayalew 1I

So enthalpy is a state function just because the components to make it up are state functions? Is there a more qualitative explanation why enthalpy is a state function?

Beza Ayalew 1I

Is there one that is more commonly given in problems or are they used equally?

Beza Ayalew 1I

ok thanks guys, so what I got from that was the major concept is that because steam requires a phase change when in contact with the skin but liquid water doesn't, the energy needed to complete the phase change results in more burns.

Beza Ayalew 1I

I think Wilson Yeh wants to know of there is a standard equation that can be applied to situations involving heat or other not state properties that we will have to know? or is the value subjective depending on the situation?

Beza Ayalew 1I

Hey, could someone please clarify why steam burns are worse than others? I know part of the explanation is that it takes around 40kJ to break liquid water bonds into water vapor, so is the reasoning just that the steam is holding in all that excess energy which causes more severe burns or not?

Beza Ayalew 1I

While thinking of that, try not to neglect the topics from before the midterms, especially since some like combustion with unknown compound X are worth a lot of points per problem.

Beza Ayalew 1I

Where can we get this table this year since there is no course reader, is it on the chemistry website or in the textbook?

Beza Ayalew 1I

I am too. I noticed a trend with strong acids including H attached to group 17 atoms(Cl, Br, ect), but HF isn't included so I don't know if HF is a strong acid or not?

Beza Ayalew 1I

And I think if there is a larger K than Q, then the equation is going in the forward direction (or to the right) because equilibrium favors the creation of more products?

Beza Ayalew 1I

And if there are no gas or aqueous solutions on one side of the equation, for example on the products side, we would use 1 as the numerator, right?

Beza Ayalew 1I

Correct me if I'm wrong, but is hybridization why you can have lewis structures where the central atom doesn't follow the octet rule after the third row?

Beza Ayalew 1I

You can't judge all acids and bases through bronsted right? I think I remember Lavelle saying Lewis Acids and Bases explain more situations of acids and bases?

Beza Ayalew 1I

When is aqua vs hydrate used?

Beza Ayalew 1I

So generally, an atom can have a formal charge of zero but an oxidation number of, for example, 2-?

Beza Ayalew 1I

Hey, this is really minute but should I be worried if my midterm grade isn't up on myucla? I figure it's fine since I got my exam back but is everyone else's score on myucla?

Beza Ayalew 1I

Hey, I was just wondering if we've gone over how to actually solve for electric configuration with sigma and pi bonds or if we've just learned the conceptual things?

Beza Ayalew 1I

I read silicon and chlorine can also have an expanded octet as well

Beza Ayalew 1I

Yea, I think the priority when making a Lewis Structure is to make sure you have the right number of electrons and that the more electronegative atoms (which are the outer atoms since the central atom is usually the less electronegative atom) have an octet, which may mean the central atom doesn't ge...

Beza Ayalew 1I

Im Pretty sure he still has videos covering certain topics under the audio visual modules, so you can use those to relearn some concepts as well.

Beza Ayalew 1I

When drawing Lewis structures of ionic bonds on an exam, do you think would we lose points for not having a plus or minus in the top right corner like Lavelle had in class even if we have the right dot structure?

Beza Ayalew 1I

Overall, memorizing with some type of correlation or rhyme would probably help with remembering which name goes with which, like I find myself remembering how charges associate with metals or nonmetals but I just mix up the names

Beza Ayalew 1I

Yea, it would be good to know the mass of an electron just as common chem knowledge, but I'm pretty sure he gave the mass of a proton, neutron and an electron on the last exam so you should generally be able to find the mass on the actual exam.

Beza Ayalew 1I

So say you have a problem asking for all of the possible quantum numbers given n=6. We know the limits of l are from 0 to n-1, but realistically, we only know that l=0 corresponds with the s orbital, l=1 with p orbital ect, so would it still be technically correct to put l=5 even though we don't kno...

Beza Ayalew 1I

On that note, does anyone know what Einstein called photons during his experimental process or did he just call them generic particles? And did he think they were a unique type of particle, or something that was already established?

Beza Ayalew 1I

Hey, One more small thing to also remember is that in general, energy is proportional to frequency and is inversely proportional to wavelength, remembering this makes solving problems where you're asked a problem with 2-3 frequencies or energy levels a lot easier, especially because you kind of know...

Beza Ayalew 1I

Also, does anyone know why carbon-12 in particular was chosen over other elements or other isotopes of Carbon?

Beza Ayalew 1I

I like to think a moles as a way to have different elements and compounds on the same page since an atom of each element on the periodic table weighs something different, so by converting grams of different molecules to moles, you can get a true image of how much you have of one compound or element ...

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